给定一个包含多个字符串的大型文本文件，读取文本文件并计算 C++ 中每个单词出现次数的最有效方法是什么？文本文件的大小是未知的，所以我不能只使用一个简单的数组。此外，还有另一个问题。此文本文件的每一行都以一个类别关键字开头，以下单词是该类别的特征。我需要能够计算每个单词在该类别中出现的次数。
例如：
colors red blue green yellow orange purple
sky blue high clouds air empty vast big
ocean wet water aquatic blue
colors brown black blue white blue blue
在这个例子中，我需要计算在“颜色”类别中，有 4 次出现“蓝色”，尽管总共出现 6 次蓝色。
我会使用流来读取和分隔单词（它通过查找空格来分隔单词）并将它们保存到字典中（标准 C++ 方法是使用std::map）。
这是一个 C++ 记录的代码：
#include <iostream>
#include <map> // A map will be used to count the words.
#include <fstream> // Will be used to read from a file.
#include <string> // The map's key value.
using namespace std;
//Will be used to print the map later.
template <class KTy, class Ty>
void PrintMap(map<KTy, Ty> map)
{
typedef std::map<KTy, Ty>::iterator iterator;
for (iterator p = map.begin(); p != map.end(); p++)
cout << p->first << ": " << p->second << endl;
}
int main(void)
{
static const char* fileName = "C:\\MyFile.txt";
// Will store the word and count.
map<string, unsigned int> wordsCount;
{
// Begin reading from file:
ifstream fileStream(fileName);
// Check if we've opened the file (as we should have).
if (fileStream.is_open())
while (fileStream.good())
{
// Store the next word in the file in a local variable.
string word;
fileStream >> word;
//Look if it's already there.
if (wordsCount.find(word) == wordsCount.end()) // Then we've encountered the word for a first time.
wordsCount[word] = 1; // Initialize it to 1.
else // Then we've already seen it before..
wordsCount[word]++; // Just increment it.
}
else // We couldn't open the file. Report the error in the error stream.
{
cerr << "Couldn't open the file." << endl;
return EXIT_FAILURE;
}
// Print the words map.
PrintMap(wordsCount);
}
return EXIT_SUCCESS;
}
输出：
空气：1
水生：1
大：1
黑色：1
蓝色：6
棕色：1
云：1
颜色：2
空：1
绿色：1
高：1
海洋：1
橙色：1
紫色：1
红色：1
天空：1
广阔： 1
水：1
湿：1
白：1
黄：1
标记单词并将它们存储为键值对。
更新：我意识到我误读了这个问题。以下代码应按类别分开和计数：
#include <iostream>
#include <string>
#include <map>
#include <fstream>
using namespace std;
int main()
{
ifstream file;
file.open("path\\to\\text\\file");
if(!file.is_open()) return 1;
map<string, map<string, int> > categories;
while(file.good())
{
string s;
getline(file, s);
int pos = s.find_first_of(' ');
if(pos < 0) continue;
string word = s.substr(0, pos);
string category = word;
s = s.erase(0, pos+1);
while(s.size() > 0)
{
pos = s.find_first_of(' ');
if(pos < 0)
pos = s.size();
string word = s.substr(0, pos);
if(word != "")
categories[category][word]++;
s = s.erase(0, pos+1);
}
}
for(map<string, map<string, int> >::iterator cit = categories.begin(); cit != categories.end(); ++cit)
{
cout << "Category - " << cit->first << endl;
for(map<string, int>::iterator wit = cit->second.begin(); wit != cit->second.end(); ++wit)
cout << "\tword: " << wit->first << ",\t" << wit->second << endl;
}
return 0;
}
更新 2：克里斯要求修改算法：
#include <iostream>
#include <string>
#include <map>
#include <fstream>
using namespace std;
int main()
{
ifstream file;
file.open("D:\\Documents\\txt.txt");
if(!file.is_open()) return 1;
map<string, int> categories;
while(file.good())
{
string s;
getline(file, s);
int pos = s.find_first_of(' ');
if(pos < 0) continue;
while(s.size() > 0)
{
pos = s.find_first_of(' ');
if(pos < 0)
pos = s.size();
string word = s.substr(0, pos);
if(word != "")
categories[word]++;
s = s.erase(0, pos+1);
}
}
for(map<string, int>::iterator wit = categories.begin(); wit != categories.end(); ++wit)
cout << "word: " << wit->first << "\t" << wit->second << endl;
return 0;
}
这是实现您既定目标的解决方案。看到它住在这里。
它std::map用于维护（类别，单词）对出现的次数。
std::istringstream用于将数据首先分解为行，然后分解为单词。
输出：
(colors, black) => 1
(colors, blue) => 4
(colors, brown) => 1
(colors, green) => 1
(colors, orange) => 1
(colors, purple) => 1
(colors, red) => 1
(colors, white) => 1
(colors, yellow) => 1
(ocean, aquatic) => 1
(ocean, blue) => 1
(ocean, water) => 1
(ocean, wet) => 1
(sky, air) => 1
(sky, big) => 1
(sky, blue) => 1
(sky, clouds) => 1
(sky, empty) => 1
(sky, high) => 1
(sky, vast) => 1
程序：
#include <iostream> // std::cout, std::endl
#include <map> // std::map
#include <sstream> // std::istringstream
#include <utility> // std::pair
int main()
{
// The data.
std::string content =
"colors red blue green yellow orange purple\n"
"sky blue high clouds air empty vast big\n"
"ocean wet water aquatic blue\n"
"colors brown black blue white blue blue\n";
// Load the data into an in-memory table.
std::istringstream table(content);
std::string row;
std::string category;
std::string word;
const char delim = ' ';
std::map<pair<std::string, std::string>, long> category_map;
std::pair<std::string, std::string> cw_pair;
long count;
// Read each row from the in-memory table.
while (!table.eof())
{
// Get a row of data.
getline(table, row);
// Allow the row to be read word-by-word.
std::istringstream words(row);
// Get the first word in the row; it is the category.
getline(words, category, delim);
// Get the remaining words in the row.
while (std::getline(words, word, delim)) {
cw_pair = std::make_pair(category, word);
// Maintain a count of each time a (category, word) pair occurs.
if (category_map.count(cw_pair) > 0) {
category_map[cw_pair] += 1;
} else {
category_map[cw_pair] = 1;
}
}
}
// Print out each unique (category, word) pair and
// the number of times that it occurs.
std::map<pair<std::string, std::string>, long>::iterator it;
for (it = category_map.begin(); it != category_map.end(); ++it) {
cw_pair = it->first;
category = cw_pair.first;
word = cw_pair.second;
count = it->second;
std::cout << "(" << category << ", " << word << ") => "
<< count << std::endl;
}
}